Last Monday, when the eastern Congolese city of Goma once again fell into the hands of an armed group – this time the M23 movement – I had a clear sense of history repeating itself. The name may have changed, but the play and many of its leading characters remain the same – arguably the most brutal and tragic situation anywhere in the world during the last 20 years.

Reports suggest that the fall of Goma has been accompanied by the killing and wounding of scores of civilians – many of them children – during the fighting over the past few days. Tens of thousands of civilians have fled, and many journalists, human rights defenders, and local officials have received death threats from M23 elements.

The fall of Goma is the latest episode in a longstanding cycle of conflict centred on the huge mineral wealth and fertile land of this part of the eastern Democratic Republic of the Congo. Over the years, ruthless leaders from within and outside Congo have employed local militias, rebel movements and members of the Congolese army itself, as well as several generations of child soldiers, to gain control of the most lucrative areas. They have consistently used terror, rape and extreme sexual violence as their primary weapons, resulting in untold misery and massive violations of basic human rights for millions.

In 2010, my office published a 550-page report that outlined 617 violent incidents in the DRC from 1993 to 2003, each one involving possible gross violations of international human rights or humanitarian law. One of the most notable of the myriad groups committing grave crimes during that decade of constant conflict was the Alliance des Forces Démocratiques pour la Libération du Congo-Zaire (AFDL), which – among other crimes – violently dismantled refugee camps in the eastern Kivu provinces in October 1996, culminating in several large-scale massacres.

The report also notes how, from 1998 to 2003, members of another Goma-based rebel movement, known as the Rassemblement Congolais pour la Démocratie (RCD), also subjected civilians to numerous murderous attacks.

A few years later, following the 2006 national elections, many fighters who had fought with these groups started yet another rebel movement, the Congrès Nations pour la Défense du Peuple (CNDP), which carried out mass killings in 2008 in the villages of Kalonge and Kiwanja under the command of Bosco Ntaganda, who has been indicted by the international criminal court.

Today, Ntaganda is still at large, and is one of the M23 movement's top leaders. The group, which includes many other suspected CNDP and RCD war criminals, is led by some of the worst violators of human rights in the world, with appalling track records including responsibility for massacres and involvement in mass rapes. Not surprisingly, since M23 first emerged in April, the UN human rights teams in DRC have documented numerous killings of civilians and other violations, including the forced recruitment of children, which may amount to international crimes.

As demonstrated in the UN expert panel report, published on Wednesday, and in earlier UN reports, the M23 and the other groups named above have all received some degree of support from neighbouring countries, including Rwanda, with devastating and widespread consequences for the human rights situation in DRC.

External state support to a group led by war criminals is totally unacceptable, and clearly contravenes UN security council resolutions. Given the appalling criminal record of many M23 leaders, alarm bells should be ringing loud and clear, but once again international attention has been tepid.

The Congolese army has itself been responsible for many grave human rights violations. Earlier this week, soldiers fleeing Goma took time off to loot the homes of the civilians they were supposed to be protecting. One of the main reasons behind its poor record is the repeated integration, in the lulls after various rebellions, of the leaders of the AFDL, RCD and CNDP rebel movements.

Peace will only take root if the leaders of DRC and neighbouring countries jointly decide to make it happen and, in particular, show genuine resolve to end the devastating impunity of serial human rights violators, whether they belong to rebel groups or the Congolese army. In their summit, scheduled for Saturday in Kampala, those heads of state and international parties who support the talks must work jointly to ensure M23 commanders responsible for war crimes find themselves behind bars, not reintegrated once again into the Congolese army, running gold mines, or enjoying the looted spoils of long-suffering Goma.